High quality austenitic stainless steel. Patented, race-winning XR-1 Raceline technology. 3 options: Offset - Made with the same patented, flow through design as the XR-1 Sportsman oval. The inlet/outlet are offset to the same side of the muffler, to accommodate transmission and frame rail interference on some applications Oval -- BORLAs #1 selling racing muffler. Satisfies the needs of most racing applications because it is the lightest, most compact, and highest flowing racing muffler in its class and at a competitive price. Record-holder Hurley Blakeney has run BORLAs on his AA/AT Ford T-Bird because he loves the quieter driver compartment without giving up any power.Round - Made with the same patented, flow through design as the XR-1 Sportsman Oval. This Muffler is 5 inches in diameter and 15 inches long. Designed for door car/ roadster applications that require a compact round muffler.